Chapter 222: Heartbeats

Dojin Frontier Autonomous Aviation Technology Research Institute.

A cylindrical structure measuring 68 meters in length and 4.5 meters in diameter stood in the center of the massive hangar.

It was the first-stage propulsion unit of Leviathan, the next-generation reusable launch vehicle.

Director Kim Se-bin displayed a 3D blueprint on the screen.

“As you can see, we’ve completed the design for pressure distribution in the propellant tank. The issue is that to enable reusability, we need to increase the structural load by at least 12% from the current level.”

The current aluminum-lithium alloy couldn’t meet the lifecycle criteria.

A tall Russian man, standing at 190 cm, approached Director Kim Se-bin.

With broad, bear-like shoulders, he wore a shirt printed with engine diagrams over his work clothes.

He was Ivan Petrovich, who had participated in the development of the improved Russian RD-171M launch vehicle.

He pointed to the bottom of the engine with his thick fingers.

“To enable more than two reignitions, we need to completely redesign the turbopump blade structure. Otherwise, chamber pressure could become unstable during the second heartbeat.”

In Russia, reignition was likened to a “second heartbeat.”

It was such a delicate and dangerous technology.

Kim Se-bin sighed deeply.

“If we remake the turbopump with a titanium alloy, the problem will be solved. But the cost will increase significantly, and production time will extend by at least two months.”

I shook my head, pointing to a part of the blueprint.

“It’s because you’re insisting on titanium alloy that both cost and time are increasing. If we make only the blade root with titanium 6Al-4V alloy and the rest of the wing with CMC (ceramic matrix composites), we can solve it in fifteen days.”

We could also reduce the cost to about a tenth.

Both men’s eyes turned to me simultaneously.

CMC was an advanced material used only in some parts in the aerospace field due to its high-temperature resistance and lightness but was difficult to process.

Ivan narrowed his eyes and asked,

“CMC is strong against thermal shock but weak against vibration fatigue. It won’t be easy to withstand the vibrations just before landing.”

I displayed a plume impingement simulation video on the screen.

“That’s why we’ll install an active deflector that adjusts the plume angle in real time just before landing. If we prevent the exhaust flow from directly impacting the blades, we can solve the vibration fatigue problem as well.”

“And if I assemble the active deflector myself, the effect will double.”

Kim Se-bin asked, looking slightly surprised,

“Then where do you plan to put that logic?”

“Of course, it has to be integrated with Luna. Only Luna can receive the lower fuselage sensor data every 0.05 seconds, control the deflector hydraulic module, and handle landing gear position correction all at once.”

It was barely at the beta version (kernel 2.0) level.

But with Black Robin production, performance was also upgrading rapidly.

By the time Leviathan was completed, it would be able to deliver sufficient performance.

“Definitely, doing it that way would enable up to three reignitions.”

As mentioned earlier, reignition wasn’t just about relighting the fire once.

Given the nature of space,

the conventional method using cryogenic fuel required stabilizing fuel temperature, pressure, and position.

In zero gravity, if bubbles or gas layers formed, the turbopump could idle, causing the engine to shut down or, worse, the chamber to explode.

“I understand that Spade Z also limited the number of reignitions due to that issue.”

To avoid vaporizing the fuel, tank insulation, pressure adjustment, and bubble removal had to be done simultaneously.

It wasn’t as easy as it sounded.

“That’s why reignition is essential in reusable launch vehicles but also the biggest barrier.”

Ivan pointed to the return trajectory sequence on the blueprint.

“To recover the first stage, immediately after separation during high-speed descent, we need to reduce speed with an ‘entry burn’ and then fully brake with a ‘landing burn’ just before touchdown. That’s at least two, and depending on the situation, three or more are needed. If you add low-orbit satellite repositioning or emergency maneuvers, the number increases further.”

The number of stable reignitions determined the recovery rate.

“The Leviathan we’re building can handle up to five reignitions.”

Startled by the sudden statement, Ivan’s eyes widened.

“What… did you say? Five reignitions are possible?”

Last year, even Spade Z, which successfully landed Marin, could only handle three reignitions.

And now, a company with no launch vehicle experience claims to enable five.

Ivan’s disbelief was understandable.

I reminded him of something he seemed to have forgotten.

“What do you think was the first thing I did when I started the Leviathan project?”

“…Yes?”

Still bewildered, Kim Se-bin answered for Ivan.

“Spade Z’s Marin uses a methane and liquid oxygen combination, but we’ve decided to use the hypergolic combination of Unsymmetrical Dimethylhydrazine (UDMH) and Dinitrogen Tetroxide (N₂O₄), along with a high-temperature ceramic nozzle.”

“Ah, right. You said you eliminated the toxicity issue of hypergolic fuels with ECR (Enhanced Catalytic Reformer) technology!”

If the toxicity issue was resolved, there was no better choice for a launch vehicle fuel than hypergolic.

It required no separate igniter like cryogenic fuel and enabled automatic ignition upon contact with the oxidizer.

The reignition sequence simplified, and fuel status could be perfectly controlled.

“Using ECR technology and hypergolic (UDMH) ultimately reduces the reignition sequence time by more than 30%, which directly relates to landing precision.”

Kim Se-bin nodded in agreement with my words.

Then, he manipulated the mouse to display an enlarged view of the variable nozzle section at the bottom of the engine.

“As you said, landing errors aren’t just due to wind or air density but because of the long time it takes to stabilize thrust after reignition. If we reduce that time, we can make finer adjustments at a much more comfortable approach angle to the barge.”

One major problem was solved, but many more remained.

Kim Se-bin displayed another blueprint with a serious expression.

“We also need to solve the shock issue that occurs during stage separation.”

The recoil during first and second stage separation was directly transmitted to the second stage’s Inertial Measurement Unit (IMU) and upper fairing frame.

This could be fatal for precise satellite deployment.

Ivan, staring intently at the blueprint, crossed his arms and shared his opinion.

“Using a gas pressure separation module instead of separation bolts could reduce the shock, but it would increase weight and significantly raise production difficulty.”

I shared the same thought.

Actually, I had seen the previous issue in Merk’s memoir before regression.

But I hadn’t deeply examined how Spade Z solved this problem.

However, my long experience as a developer brought an answer to mind.

“A way to manage both cost and weight.”

“Instead of compressed gas or explosive bolts, how about using dual magnetic separation rings? They maintain the coupled state with high-energy electromagnets and generate repulsive force by cutting the current at the moment of separation.”

Hearing this method for the first time, Ivan frowned.

“It seems like a method never used in commercial launch vehicles?”

“It hasn’t been used in launch vehicles, but it’s a technology already proven in combat aircraft weapon separation devices. It’s less than half the weight of explosive bolts and reusable.”

Listening to me, Kim Se-bin, who had been calculating something, suddenly exclaimed.

“Definitely, with that method, the separation shock acceleration would drop below 10G… no, almost certainly.”

Ivan’s eyes widened in surprise.

“If that’s true… it’s incomparable to the 80-100G shock of explosive bolts. At that level, much of the Inertial Measurement Unit (IMU) calibration error would disappear.”

Ivan unfolded his arms and leaned toward me.

“And if it’s reusable, maintenance costs would significantly decrease. But… to perfectly distribute the magnetic repulsive force on both sides, the rings would need precise machining. Is that possible?”

I smiled and pointed to the opposite side of the hangar with my finger.

“Using the 5-axis milling machine over there, we can achieve precision up to ±0.001mm. And by controlling the electromagnet current in real time with Luna, we can perfectly synchronize the repulsive force on both sides of the ring.”

“I’ll run the simulation right now…”

Feeling the possibility, Kim Se-bin immediately input the virtual parameters for the magnetic separation ring.

As the simulation ran, a graph appeared on the screen.

0.00 seconds: Electromagnet released, repulsive force generated

0.04 seconds: First and second stages fully separated

Maximum shock acceleration: 8.7G

Residual vibration damping time: 0.15 seconds

Comparison data for the conventional explosive bolt method appeared alongside on the screen.

Maximum shock acceleration: 92.4G

Residual vibration damping time: 1.43 seconds

The difference was clear not only in the numbers but also in the high-speed camera simulation video.

With the explosive bolt method, the second stage’s lower part shook violently at the moment of separation, and the fairing frame bent, but with the magnetic separation ring, the coupling line broke cleanly, and the frame deformation rate was only 0.02mm.

Kim Se-bin swallowed hard, looking at the screen.

“This… it’s not just shock mitigation, but the stability exceeds what’s required for precise satellite deployment levels.”

Ivan, narrowing his eyes and staring at the monitor, unconsciously spoke in Russian.

“Боже мой (My God)… With these numbers, we won’t need to recalibrate the expensive IMU (Inertial Measurement Unit) and can reuse it immediately.”

He soon turned to me, spreading his hands.

“Using the method you mentioned, we can definitely create a launch vehicle surpassing the Marin made by Spade Z.”

“Not ‘definitely,’ but we must make it so.”

That’s why we spent astronomical amounts to bring people like Ivan here.

Of course, due to bringing talent from many countries, integration wasn’t going smoothly yet.

Before full-scale propulsion unit production, we decided to solve that issue first.